1. Field of the Invention
This invention relates to a process for the preparation of an N-silylorganocarbamate from an aminoorganosilane and organocarbonate ester employing a basic catalyst.
2. Description of the Related Art
Organocarbamates have found widespread utility in such application as pesticides, herbicides, and pharmaceuticals, as well as their use in the manufacture of polyurethane foams, coupling agents and adhesion promoters. Although a number of methods currently exist for the synthesis of silylorganocarbamates, the simultaneous production in these processes of byproducts termed xe2x80x9cheaviesxe2x80x9d, as well as the generation of large quantities of hazardous wastes has proved to be problematic for their use in all but a few applications. Thus, there continues to be a need for a process that will produce an organocarbamate without the resultant production of toxic and corrosive heavies.
Typically, the reaction of an aminoorganosilane and an organocarbonate ester in the presence of an alcoholate catalyst is conducted at low temperatures, i.e., 25xc2x0 to 50xc2x0 C. and over long periods of time, i.e., 4 to 6 hours. The process of preparing carbamates from primary amines without using volatile byproduct producing chloroformates has also been reported. Several processes also describe the manufacture of carbamates by the oxidative carbonylation of amines with carbon monoxide (CO) in the presence of transition metal compound catalysts such as palladium (Pd), ruthenium (Ru), and manganese (Mn). They can also be formed by the reductive carbonylation of nitro compounds such as nitrobenzene with alcohols and CO in the presence of Ru, rhodium (Rh), and/or Pd compounds. It has also been reported that azides are transformed into various carbamates by using Me3P and commercially available chloroformates.
Carbamates can be formed from the direct reaction of primary amines and organocarbonates such as dimethyl carbonate (DMC). European Patent No. A 391,473, for example, describes a process for producing carbamates using reduced amounts of catalyst by first reacting a suitable amine with a cycloalkyl carbonate in the presence of a carbamation catalyst to produce a mixture of carbamates and a urea. Further reaction of the urea with the carbonate produces the corresponding carbamates, which are eventually recovered from the reaction mixture.
In German Patent No. A 3,202,690 a process for preparing aromatic urethanes is described by the reaction of aromatic amines and alkylcarbonates in the presence of an alcoholate of an alkali metal or an alkaline earth metal.
More recently, a method of preparing carbamates has been described in U.S. Pat. No. 5,962,721 to Kim et al., by reacting an amine with an alcohol and a mixed gas of CO/O2 in the presence of one or more monovalent copper catalysts.
Japanese unexamined Patent Publication No. 311452/1990 discloses a process for using a base as a catalyst in which an alcoholate of a suitable alkaline metal and alkaline earth-metal is employed. However, the base prepared by this method remained in the carbamate and thus must be removed by neutralization to prevent polymerization and/or coloration during the conversion of carbamate to isocyanate.
Alternatively, silylcarbamates have also been prepared by the reaction of a suitably functionalized silylorgano halide, a metal cyanate, and monohydridic alcohol in the presence of an aprotic solvent such as N,N-dimethyl formamide. Unfortunately the necessity for large quantities of expensive solvent and yields that do not typically exceed 85% currently make this process less economically attractive.
Silyl carbamates have also been prepared through the hydrosilation of suitably functionalized allyl carbamates and allyl isocyanates with trimethoxy silane as reported in U.S. Pat. No. 5,220,047. The commercial availability of allyl carbamates and or allyl isocyanates, however, has severely limited the commercial viability of this process.
Silylorganocarbamate formation has also been obtained from the direct reaction of a suitable dialkyl carbonate and the corresponding aminoorganosilane in the presence of a basic catalyst such as sodium methylate. See, in this regard, U.S. Pat. No. 5,218,133 the contents of which are incorporated herein by reference. The tendency of dialkyl carbonates to alkylate the amino functionality at elevated temperatures, however, produces an undesired side product and reduces the yield of the silylcarbamate.
According to the process described in aforementioned U.S. Pat. No. 5,218,133 the aminoorganosilane was combined with a mixture of dimethyl carbonate and sodium methoxide at ambient temperature over 30 minutes and held at this temperature for an additional 3 hours during which a reaction producing methyl N-3-(trimethoxysilyl)propylcarbamate took place. The reaction mixture was then heated to 50xc2x0xc2x15xc2x0 for an additional hour to complete the reaction
It is an object of the present invention to provide a process for preparing an N-silylorganocarbamate, which can be used as a reactant in the further process of preparing an isocyanurate.
It is a further object of the present invention to provide the aforementioned process of preparing an N-silylorganocarbamate that can be utilized at an elevated temperature to increase the reaction rate while minimizing unwanted byproduct formation and thus resulting in greatly improved yield of the desired N-silylorganocarbamate.
In keeping with these and other objects of the invention, there is provided a process for preparing an N-silylorganocarbamate which comprises:
(a) providing a mixture of aminoorganosilane of the general formula:
R3nR23xe2x88x92nSiR1NH2
wherein R1 is a divalent hydrocarbon group of from 1 to about 20 carbon atoms; R2 and R3 each is independently an alkyl group containing from 1 to about 20 carbon atoms, an alkoxy group containing from 1 to about 20 carbon atoms, an aryl group containing from about 6 to about 10 carbon atoms, or an aryloxy group containing from about 6 to about 10 carbon atoms with at least one of R2 and R3 being a hydrolysable alkoxy group; and where n is 0 to 3, and a catalytically effective amount of basic catalyst and;
(b) combining the mixture of aminoorganosilane and basic catalyst with an organocarbonate ester of the general formula:
R4OC(O)OR4
wherein each R4 is independently the same or different hydrocarbyl group of up to about 20 carbon atoms or halohydrocarbyl group of up to about 20 carbon atoms, or both R4 groups together form a divalent alkylene group R5 of from 2 to about 6 carbon atoms, the mixture of aminoorganosilane and basic catalyst, the organocarbonate ester or both being at elevated temperature at the time of their being combined, thereby producing N-silylorganocarbamate of the general formula:
R3nR23xe2x88x92nSiR1NHC(O)OR6
wherein R1, R2 and R3 have the aforestated meanings and R6 is R4 or R5H in which R4 and R5 have the aforestated meanings.
In contrast to the process described in U.S. Pat. No. 5,218,133, supra, in which aminoorganosilane is combined with a mixture of dimethyl carbonate (an organocarbonate ester) and a basic catalyst such as sodium methoxide (an alcoholate) at ambient temperature with the temperature of the reaction medium being increased only in the terminal phase of the reaction, the process of the present invention combines the organocarbonate with a mixture of aminoorganosilane and basic catalyst and does so with either the organocarbonate, the mixture of aminoorganosilane and basic catalyst or both being at elevated temperature at the time they are combined. As a result of this order of addition of the components of the reaction medium and the initially elevated temperature of at least the organocarbonate reactant or the mixture of the aminoorganosilane and basic catalyst, the process of this invention results in significantly increased production of the desired carbamate product.
In the process of this invention, aminoorganosilane and organocarbonate ester can be considered to react to form N-silylorganocarbamate in accordance with the reaction: 
It will be understood that when, in organocarbonate ester R4OC(O)OR4, each R4 is a different group, the reaction herein will produce a mixture of N-silylorganocarbamate products.
The aminoorganosilane used in the preparation of the N-silylorganocarbamate product of this invention is at least one compound of the general formula R3nR23xe2x88x92nSiR1NH2 wherein R1, R2, R3 and n have the aforestated meanings. Useful aminoorganosilane reactants include, for example, 3-aminopropyltrimethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-(aminopropyl)ethyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylethoxysilane, 3-aminopropylphenyldimethoxysilane, 2-aminoethyltriethoxysilane, 4-aminobutyltriethoxysilane, 4-aminobutyltrimethoxysilane, 4-aminobutylmethyldimethoxysilane, 4-(trimethoxysilyl)-2-butanamine, 3-[diethoxy(hexyloxy)silyl]-1-propanamine, 3-[tris(pentyloxy)silyl]-1-propanamine, 3-[tris(2,2,2-trifluoroethoxy)silyl]-1-propanamine, 3-[tris[2-(2-phenoxyethoxy)ethoxy]silyl]-1-propanamine, 3-[tris[(2-ethylhexyl)oxy]silyl]-1-propanamine, 3-[tris(hexyloxy)silyl]-1-propanamine, 3-triisopropoxysilylpropylamine, 3-[tris(3-methylbutoxy)silyl]-1-propanamine, 3-[tris(2-ethoxyethoxy)silyl]-1-propanamine, 3-[bis(1,1-dimethylethoxy)methoxysilyl]-1-propanamine, 3-[(1,1-dimethylethoxy)diethoxysilyl]-1-propanamine, 3-[(1,1-dimethylethoxy)dimethoxysilyl]-1-propanamine, 3-(trimethoxysilyl)-1-pentanamine, 10,10-bis[2-(2-ethoxyethoxy)ethoxy]-3,6,9-trioxa-10-silatridecan-13-amine, and 13,13-bis[2-[2-(2-ethoxyethoxy)ethoxy]ethoxy]-3,6,9,12-tetraoxa-13-silahexadecan-16-amine, 4-amino-3,3-dimethylbutyltrimethoxysilane, 4-amino-3,3-dimethylbutyltriethoxysilane, and the like.
The aminoorganosilane can be made by any commercially available method, and preferably by the processes of copending U.S. patent application Ser. No. 60/428,323 filed Nov. 21, 2002, or U.S. Pat. No. 6,242,627 the contents of which are both hereby incorporated by reference.
The catalyst employed herein is a strong base. Preferably, the strong base is an alkoxide (alcoholate) of an alkali metal or alkaline earth metal. Examples of useful alkoxides include sodium methoxide, sodium ethoxide, calcium methoxide, calcium ethoxide, sodium propoxide, sodium tert-butoxide, potassium propoxide, potassium tert-butoxide, lithium methoxide, lithium ethoxide, lithium propoxide, lithium tert-butoxide and the like.
In general, the amount of basic catalyst employed in the process of this invention can range from about 0.01 parts by weight to 2 parts by weight per 100 parts by weight of the aminoorganosilane and organocarbonate ester. Preferably, the amount of basic catalyst ranges from about 0.2 to 0.6 parts by weight per 100 parts by weight of the aminoorganosilane and organocarbonate ester.
The aforementioned combination of aminoorganosilane and basic catalyst is combined with at least one organocarbonate ester of the general formula R4OC(O)OR4 wherein each R4 has the aforestated meaning. Useful organocarbonate esters include, for example, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, dihexyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, diphenyl carbonate, methyl phenyl carbonate, ethylene carbonate, propylene carbonate, and the like and mixtures thereof.
The reaction of the aminoorganosilane with the organocarbonate ester can be carried out using stoichiometric amounts of these reactants. However, preferably, an excess of the organocarbonate ester, e.g., from about 0.05 to about 1 mole of organocarbonate ester, per mole of aminoorganosilane can be employed in the reaction. Most preferably, from about 0.1 to about 0.4 moles of excess organocarbonate ester per mole of aminoorganosilane is employed.
A principal advantage of the process of the present invention, namely, increased production of carbamate, depends upon the manner of addition of the components of the reaction medium and their temperature at the time of their combination. Specifically, the aminoorganosilane must first be mixed together with the basic catalyst prior to the resulting mixture being combined with the organocarbonate ester reactant. The requirements of the step of combining the mixture of aminoorganosilane and basic catalyst and the organocarbonate ester are satisfied by (1) combining the mixture of aminoorganosilane with an basic catalyst at elevated temperature with the organocarbonate ester at ambient temperature, or (2) combining the mixture of aminoorganosilane and basic catalyst at ambient temperature with the organocarbonate ester at elevated temperature, or (3) combining the mixture of aminoorganosilane and basic catalyst at elevated temperature with the organocarbonate ester at elevated temperature.
The advantages of the process of this invention lie not only in the increased production of carbamate but also in the significant reduction in byproducts which are commercially termed xe2x80x9cheaviesxe2x80x9d. The reaction from the start is carried out at elevated temperature thus substantially accelerating the reaction and increasing the yield of the desired N-silylorganocarbamate product.
As indicated above, the process herein is carried out with the mixture of aminoorganosilane and basic catalyst, the organocarbonate ester or both being at elevated temperature, preferably from about 50xc2x0 to about 150xc2x0 C. and more preferably from about 70xc2x0 to about 110xc2x0 C., at the time of their combination. The process can be carried out at ambient, sub-atmospheric or super-atmospheric pressure.
The process can be carried out in either a batch or continuous-feeding process of adding either the aforementioned mixture of aminoorganosilane and basic catalyst to the organocarbonate ester all at once or through a gradual feeding of the organocarbonate ester that can last from about 5 minutes to up to about 4 hours, wherein preferably, the continuous feeding is accompanied by the recycling of excess organocarbonate ester.
Upon completion of the reaction, the solution of product organocarbamate, the catalyst, the byproduct alcohol, and excess organocarbonate ester is neutralized with an acidic agent to significantly reduce the basicity and can even result in creating an acidic solution. The preferable acidic agent can be any Lewis acid but more preferably includes inorganic acids such as anhydrous phosphoric acids and most preferably organic acids such as glacial acetic acid, propionic acid, butyric acid, hexanoic acid, oleic acid, maleic acid, fumaric acid, succinic acid and the like and combinations thereof. The absence of water in the inventive process is desirous to avoid unwanted reactions and byproducts.
The aforementioned product solution can be additionally filtered and/or stripped using any known commercially available means such as vacuum or pressure filtration to remove the byproducts or volatile heavies. This filtration and/or stripping can occur either simultaneously with the neutralization or immediately thereafter.
In the product N-silylorganocarbamate R3nR23xe2x88x92nSiR1NHC(O)OR6, R1 is preferably a divalent group of an alkane, cycloalkane, aromatic or aralkane compound, for example, the same or different linear or branched alkylene group such as methylene, ethylene, 1,2-propylene, 1,3-propylene, 2-methyl-1,3-propylene, 3-methyl-1,3-propylene, 3,3-dimethyl-1,3-propylene, ethylidene, isopropylidene, 3-methyl-1,4-butylene, 3,3-dimethyl-1,4-butylene, and the like; the R2 and R3 groups are preferably independently selected to be alkyl, aryl, acetoxy or alkoxy groups of up to about 20 carbon atoms with at least one of R2 and R3 being an alkoxy group; R6 is preferably the group R4, the latter preferably being a lower alkyl, lower haloalkyl or aryl group, or the group xe2x80x94R5H with R5 being ethylene (xe2x80x94CH2CH2xe2x80x94). More preferably, the R2 and R3 groups can be, for example, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, pentyl, dodecyl, methoxy, ethoxy, propoxy, isopropoxy, butoxy, phenyl or phenoxy. The R2 and R3 groups are most preferably selected from the group consisting of methyl, methoxy, ethyl, and ethoxy, and the like, and mixtures thereof. Whatever the nature of the R2 and R3 groups, at least one of these groups must be an alkoxy group, for example, any of the aforerecited alkoxy groups.
Specific N-silylorganocarbamates that can be prepared in accordance with this invention include N-(3-trimethoxysilylpropyl)methylcarbamate; [3-(triethoxysilyl)propyl]-carbamic acid nonadecyl ester; [3-(triethoxysilyl)propyl]-carbamic acid 2-[2-(2-methoxyethoxy)ethoxy]ethyl ester; carbonic acid 1,1-dimethylethyl 3-[[[[3-(triethoxysilyl)propyl]amino]carbonyl]oxy] phenyl ester; [3-(triethoxysilyl)propyl]-carbamic acid 3-phenyl-2-propenyl ester; [3-(triethoxysilyl)propyl]-carbamic acid 3,3-diphenyl-3H-naphtho[2,1-b]pyran-9-yl ester; [3-(ethoxydimethoxysilyl)propyl]-carbamic acid methyl ester; [3-(diethoxymethoxysilyl) propyl]-carbamic acid methyl ester; [3-(triethoxysilyl)propyl]-carbamic acid 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl ester; [3-(triethoxysilyl)propyl]-carbamic acid 1,3,5-benzenetriyltris(methylene) ester; [3-(triethoxysilyl)propyl]-carbamic acid 1,3,5-benzenetriyltris(methylene) ester; [3-(triethoxysilyl)propyl]-carbamic acid phenylmethyl ester; [3-(trimethoxysilyl)propyl]-carbamic acid ethyl ester; [3-(trimethoxysilyl)propyl]-carbamic acid 1,1-dimethylethyl ester; [3-(triethoxysilyl) propyl]-carbamic acid 1,1-dimethylethyl ester; [3-(trimethoxysilyl)propyl]-carbamic acid methyl ester; or, [3-(triethoxysilyl)propyl]-carbamic acid ethyl ester.
The entire process or any individual step therein can be done in the presence of a dry inert gas. Such gases can include nitrogen and argon and the like or mixtures thereof.